The successful treatment of paroxysmal
supraventricular tachycardia with adenosine 5` triphosphate (ATP) was
initially reported by Somlo1 in 1955.
Sharma et al2 noted the value of
intravenous ATP in the diagnosis and management of wide QRS complex
tachycardia. ATP in incremental doses has been used for the
non-invasive diagnosis of concealed accessory pathways3.

Non-invasive diagnosis of dual AV node physiology (DAVNP) in patients
with AV nodal reentrant tachycardia by administration of ATP or
adenosine
has been reported by different authors4,5. Though many of the studies were using
incremental dosage, single dose tests with ATP6
and adenosine7 have also been useful in the
diagnosis of DAVNP.
The test is useful in sinus rhythm to establish the presence of DAVNP.
DAVNP is considered to be present when at least one of the following
events
occur following ATP injection: 1) PR interval increases or decreases by
>50 ms in 2 consecutive sinus beats; 2) an AV nodal echo beat is
observed;
3) AVNRT develops. In this issue of the Journal, Belhassen et al8 report that DAVNP is present in a relatively
high proportion (36.5%) of patients following termination of AVNRT with
ATP
but is much less frequent (5.5%) in control patients. In addition, they
show that the occurrence of DAVNP following the administration of ATP
in
sinus rhythm is a good predictor of its occurrence after termination of
AVNRT with ATP. Thus, findings at termination of tachycardia by ATP may
be useful in the noninvasive diagnosis of the mechanism of a paroxysmal
supraventricular tachycardia.

In patients with palpitations of unclear etiology, ATP test identifies
those who are likely to have AVNRT or AVRT (and who are therefore
likely
to benefit from electrophysiological evaluation) with a high positive
predictive
value9. ATP/adenosine test is also useful
in
confirming the result of radiofrequency ablation of slow pathway6,10. Among patients with no
history
suggestive of AVNRT, less than 3% have clinically silent DAVNP on
incremental
adenosine infusion11. Adenosine/ATP
infusion
can be used a simple bedside screening test for patients with symptoms
suggestive of of paroxysmal supraventricular tachycardia which is
undocumented
and in those in whom the mechanism of a narrow complex tachycardia is
unclear.
This test may be specially relevant in developing countries with
limited
resources, in selecting patients for further electrophysiological
evaluation.